A method for weaving tape-like warps and wefts, and not yarns, is described in U.S. Pat. No. 6,450,208. This method describes a novel rotor type of shedding system for manipulating the tape-like warps and a method to align the laid-in tape-like weft at the fabric-fell using a set of rollers, and not the reed. Details relating to warp feeding; weft selecting, feeding and inserting; selvedge forming; and the taking-up of the woven material are however not available. The possibility of supplying warp and weft tapes of partially stabilized fibrous type in singles or in tandem to obtain doubled warp and weft tapes and overfeeding of the same to introduce non-linearity or waves/textures in the arrangement of the fibres in the tapes are also not known from this patent. The described method of aligning the laid weft tape with rolls is adequate when the weft tapes are of sandwich/bonded/laminated type, i.e. of a joint construction. Weft aligning with such rolls cannot be achieved satisfactorily when doubled wefts are inserted because the constituent tapes of the doubled weft, which exist loose or disconnected, are free to slide relative to each other. When the rolls turn, they contact and align the facing tape as it gets laterally slipped past the rear tapes. Another drawback with the use of rolls for weft aligning is that unbounded fibres get pulled out from partially stabilized and non-stabilized types of fibrous tapes. Such weft aligning rolls are also incapable of depositing weft tapes in a slant or oblique orientation in relation to the warp tapes. Further, the fabric described therein uses warps and wefts that are of sandwich/bonded/laminated type and hence the constituent tapes are not free to slide relative to each other. Also, the fibres in the fibrous tapes are unidirectionally or linearly orientated in the longitudinal direction of the tape. The described sandwich/bonded/laminated tapes are also not composed of any tapes that comprise pre-waved/textured arrangement of fibrous materials that could be straightened by pulling the tape longitudinally to re-establish fibre linearity. Consequently such a fabric does not drape effectively when formed into curved shapes, such as a cone, pyramid, barrel, helmet etc., due to crumples/wrinkles at the inner side and stretches at the outer side respectively of the curved part. Also, openings or gaps are created between adjacent tapes. Such tape-woven fabrics thus cause uneven fibre orientation and density when the fabric is curved into a shape due to different extensibilities of the constituent materials and radii of curvatures. Also, the described fabric is flat and does not comprise sections that are relatively flat/planar and thicker/raised wide ribs resembling somewhat like a profiled material in its cross-section. Further, fabrics like those comprising slant or oblique wefts in relation to warp tapes, a formed shape within its body, and warp and weft tapes of shaped edges matched in either close or open fit configuration are not known from this patent.
A method for weaving ‘flat carbon fibre yarn’ as warp and weft is also described in U.S. Pat. No. 5,455,107. As is apparent, this modified weaving method is based on horizontal format and traditional approach that is designed for processing yarns. Consequently it has certain limitations. For example, the described method does not appear to process tape widths greater than 16 mm; it cannot feed positively variable lengths of warps in a tensionless condition; it cannot process warp and weft tapes of different widths, constructions and materials in the same fabric; it cannot take-up fabric with variable widths of wefts; there is no selvedge formation carried out, making fabric handling difficult; its working actions, especially that of beating-up with reed and taking-up fabric with so many frictional and compression points are deleterious to the warp and weft tapes of many kinds and hence adversely affect the properties and quality of the woven materials.
Further, this method processes warps and wefts of only fibrous tapes that are either wholly unglued (i.e. non-stabilized) or wholly glued (i.e. stabilized) with a sizing agent, are very thin and of relatively small widths. As a consequence, the wholly unglued fibres in the tapes are vulnerable to lateral shifting causing their bunching in some places and openings in the other. The wholly sized or stabilized fibres on the other hand are not flexible and therefore such rigid fibres cannot be overfed positively to create non-linearity in their arrangement such as waves/textures within the tape as and when required during weaving. It may be pointed out that the orientation of fibres in both stabilized and non-stabilized types used therein is unidirectional along tape length. The use of partially stabilized fibrous tapes has not been considered.
When plied wholly sized tapes are woven as described in it and the fabric curved into a shape, the plied tapes do not take corresponding different radii of curvatures to produce the shape smoothly. Crumples and stretches are produced. A further related problem with the described woven material is that the plied warps and wefts cannot slide relative to each other when formed into a curved shape because they get clutched in their positions due to the relatively frequent interlacements from the use of relatively small widths of tapes that are processed under tension and also due to the frictional forces and adherence caused by the sizing agent in the tape. This problem gets further compounded because the sizing agent on these wholly sized tapes cracks easily when curving the fabric into a shape. These cracks occur at random locations. As a consequence, the cracking of the sizing agent also causes small bunches of glued fibres to shift laterally within the tape to create openings or gaps in the shaped fabric, and sometimes even fibre breakages. Using force to slide a clutched tape that is also randomly cracked across its width results in the bunched groups of stuck fibres to shift further in lateral directions and thereby create even wider gaps/openings in the fabric. The openings created in the fabric due to separation of the glued fibres also leads to uneven fibre distribution and orientation and thereby the performance level of the woven material gets lowered. This described phenomenon also occurs when non-stabilized or wholly unsized fibrous tapes are pulled because the fibres are free and get immediately bunched or roped creating gaps and openings in the fabric. As can be understood now, it is not advantageous to use wholly stabilized fibrous tapes and non-stabilized fibrous tapes for certain applications.
Another disadvantage of the method according to U.S. Pat. No. 5,455,107 that may be mentioned here is that because no selvedge formation is carried out, handling of the woven material is rendered difficult. Without the selvedges the wholly stabilized fibrous tapes constituting the woven material are prone to come loose at the selvedge sides easily and thereby initiate the neighbouring tapes to also shift out. The lack of selvedges has an even more adverse effect when the fabric is woven with non-stabilized fibrous tapes because then fibre-bunching or roping effect is caused at slightest deformation during handling. Undesirable gaps/openings in the fabric are immediately created in the woven material.
Further, this method cannot introduce non-linearity or waves/textures in the fibres, even when weaving with non-stabilized fibrous tapes, because there is no arrangement for overfeeding the tapes and also because the method inherently requires maintaining of tensions in warps and wefts at all times to carry out weaving. Also this method cannot produce a woven material wherein the weft tapes are incorporated obliquely or slant in relation to the warp tapes. Further, the described fabric is flat and does not comprise sections that are relatively flat/planar and thicker/raised wide ribs resembling somewhat like a profiled material in its cross-section. Also, a material that has a formed shape within its body and a material made using tapes of shaped edges are not known from this patent.
The tape constructions described in, for example, U.S. Pat. No. 5,763,069 and U.S. Pat. No. 5,395,665 are also of sandwich/laminated/bonded type in construction and their constituent stacked components cannot slide relative to each other. These tapes also do not have shaped edges.
Accordingly, there is therefore a need for an improved method and means for producing woven materials of tape-like warps and wefts, and for improving such materials. For example, it is now desirable to have a method whereby a woven fabric is produced using preferably partially stabilized fibrous type of tapes to conform smoothly with the required shape during shaping. Additionally use of doubled tapes would help to cover created gaps and also obtain fabrics of variable weight per unit area. It is also desirable to have the said features in a woven material wherein the weft tapes are incorporated not only at 90° to warp tapes but obliquely or slant as well. Further, it is also desirable to produce a form in the fabric body and a fabric with tapes of shaped edges.
The unsuitability of the conventional weaving operations and also those relating to the referred patents in the context of the present invention are considered individually in the section Description of the Preferred Embodiments.